1. Field of the Invention
The present invention relates to a safety-guard detection circuit of a fan motor, and more particularly to the safety-guard detection circuit connected to a rotation detection terminal of a third lead of the fan motor to thereby avoid discharge breakdown and wire shorts at the driver IC input.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a conventional driver circuit and a conventional rotation detection circuit (phantom lines) of a dc brushless motor.
As shown in FIG. 1, the conventional motor driver circuit 1 includes a driver IC, and two coils L1 and L2. A Hall effect sensor module and a control module (transistor) are built into the driver IC. The Hall sensor is adapted to detect changes in the magnetic field of the permanent magnet of the rotor, and the weak Hall voltage is amplified by the driver IC. The two output terminals OUT1 and OUT2 of the driver IC then alternatively output current to the two coils L1 and L2 so that the two coils L1 and L2 are excited to rotate the rotor. In this time, the two output terminals OUT1 and OUT2 of the driver IC simultaneously output two opposite phase square waves. The conventional rotation detection circuit generally includes a transistor Q1, and a resistor R1 to define an amplifier circuit. The resistor R1 is connected in series to the base of the transistor Q1 and the output terminal OUT2, while the collector of the transistor Q1 is predetermined as a rotation detection terminal, as well as a third lead.
FIG. 2 is a circuit diagram of a conventional driver circuit and a rotation detection terminal of a single phase dc brushless motor. As shown in FIG. 2, the conventional motor driver circuit 1 includes a Hall sensor IC1 and a driver IC2. The output terminal of the Hall sensor IC1 is connected to the input terminal of the driver IC2. The two output terminals of the driver IC2 are connected to a coil L1. An output terminal FG of the driver IC2 is predetermined as a rotation detection terminal, as well as a third lead.
During operation of the motor driver circuit, the third lead of the driver circuit of the dc brushless motor, as shown in FIGS. 1 and 2, is provided for connecting to a rotation detection circuit. In general, the third lead is reserved and exposed to thereby facilitate assembly operation of the motor. However, during assembly operation the third lead may possibly contact with a human body. Discharge breakdown will occur through the third lead as the human body may have considerable static electricity. Thus, the driver IC or the transistor of the motor will be damaged by the static electricity. Referring again to FIG. 1, during assembly operation, if the third lead is connected to a power source, a large current is directly input into the base of the transistor Q1 or the driver IC that must damage the transistor or results in a wire short of the driver IC. To avoid the occurrence of transistor damage and driver IC wire shorts during the assembly operation, a need exists for the third lead to have a safety-guard device, thereby enhancing the reliability of the motor function.
Accordingly, the present invention may improve the above-mentioned drawbacks, by connecting a third lead and a rotation detection terminal of the motor driver to a safety-guard detection circuit. Thus, when the human body contacts with the third lead during assembly operation of the motor, the safety-guard detection circuit is adapted to limit a large current input into the motor driver through the third lead. And a discharge member, a zener diode for example, is adapted to ground the large current to thereby avoid transistor damage and driver IC wire shorts.
The primary objective of the present invention is to provide a safety-guard detection circuit for a fan motor, wherein the motor driver is connected with a safety-guard detection circuit which is adapted to limit a large current input into the motor driver through the third lead when the human body contacts with the third lead during assembly operation of the motor, to thereby avoid transistor damage and driver IC wire shorts.
In accordance with the present invention, a safety-guard detection circuit of a fan motor includes a resistor for limiting a large current from being input into a motor driver circuit, and a discharge member for grounding the large current limited by the resistor. The resistor and the discharge member are commonly connected to a third lead of the motor driver circuit.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.